I understand that increasing voltage increases the energy given to each coulomb in the circuit, so in theory more energy given to a bulb should make a bulb glow brighter. But also if voltage is constant and resistance decreases, then current increases so that means that the bulb glows brighter too because more coulombs are flowing through it per second. But what happens if voltage and resistance are increased proportionately so that current remains the same? More energy is supplied to each coulomb so it should make the bulb grow brighter right? Or have I made some error?
[Physics] Will a bulb glow brighter if voltage is increased but current remains the same
electric-currentelectrical-resistanceelectricityvoltage
Related Solutions
The current depends on the drift velocity of the electrons, in the metal lattice.
I is the electric current n is number of charged particles per unit volume (or charge carrier density) A is the cross-sectional area of the conductor v is the drift velocity, and Q is the charge on each particle.
The higher the voltage, the higher the current, from I=V/R .
In the Resistance of the lamp, the higher drift velocity electrons will interact and transfer more energy to more of the atoms/molecules of the lattice in the resistor, which will translate to more photons as the atoms/molecules relax back.
The question setter forces you to think for yourself about the possibilities. If MrX had wired some bulbs in series and some in Parallel then there would be a difference in brightness assuming all bulbs were the same wattage. Series connection of all bulbs would not be practical for 40 bulbs. MrY simply arranged all bulbs in parallel. If bulbs were of differing wattage then a combination of parallel and serial connection would be required to get equal glow from all connected bulbs. Assuming MrX bought 20 x 60W and 20 x 20W globes, MrY would have to series 60W and 20W bulbs and then put these in strings in parallel with each other. Don't over think the problem.
Best Answer
Without changing the characteristics of the light bulb, it's not possible to change the voltage if you want the current to stay the same. When the voltage is increased, the current through the bulb has to increase as well, because of Ohm's law: $I=V/R$ which means that if $V$ increases, so does $I$.
If you want the current to stay the same when the voltage increases, you need to insert additional resistance in series with the bulb's filament. That additional resistor will show a voltage drop of $V_1=I*R_1$, which is exactly the increase in applied voltage, and the voltage over the bulb will still be the same as the original. This extra resistor now dissipates the additional power.
If this extra resistor is part of the bulb's filament (so we now have a different bulb), then that extra power will make the bulb brighter, because $P=V*I$.